A new leader exon identified in the rat insulin-like growth factor II gene.

In the rat insulin-like growth factor II gene, we identified an alternative 5'-untranslated sequence, in addition to the two sequences documented recently (1986) J. Mol. Biol. 192. 737-752, (1986) J. Biol. Chem. 261. 17138-17149. This sequence was encoded in an extreme 5' separate exon (E1 exon), the promoter region of which could be distinguished from others by features including lack of the TATA-box and GC-repeat, and heterogeneity in the transcriptional initiation.